A commonly used standard packet transport protocol for the transmission of data packets over fiber links is POS, where POS is an acronym for “PPP Over SONET”, PPP is an acronym for “Point-to-Point Protocol”, and SONET is an acronym for “Synchronous Optical NETwork”.
PPP provides an encapsulation for variable length packets transmitted from a sending terminal to a receiving terminal. PPP is described in more detail in the IETF (internet engineering task force) documents RFC 1661 and RFC 1662. POS provides the adaptation of a PPP packet to meet the requirements of the SONET standard. POS is described in more detail in the IETF document RFC 2615.
Several other fiber transport protocols exist for transmitting data packets over fiber links. For example, the proposed Gigabit Ethernet WAN (Wide Area Network) standard (10 Gigabit Ethernet Technology Overview White Paper, http://www.10gea.org/10GEA_Whitepaper—0901.pdf) provides similar capabilities for carrying data packets as does the POS standard.
MPLS (Multiprotocol Label Switching) is a protocol used in high speed data packet networks to provide efficient routing and switching of packets. In an MPLS network, packets are assigned a label (by a label edge router) and forwarded along a label switched path (LSP) where each label switch router (LSR) makes forwarding decisions based on the contents of the label. One of the capabilities of MPLS is the ability to create end-to-end circuits with specific performance characteristics. The MPLS architecture is described in IETF document RFC 3031. The MPLS label mechanism is described in IETF document RFC 3032.
The Internet protocol (IP) is the most common networking protocol providing end-to-end user packet networks. MPLS networks are used to build high capacity and high performance backbone networks linking IP networks.
While MPLS and POS protocols provide the basis for building fiber based packet networks which can forward IFP user packets, there is also a requirement in such networks to provide OAM&P (Operations, Administration, Maintenance, and Provisioning) capabilities which permit the operator of the network to interrogate and control the operation of the network.
As part of the OAM&P functionality, it is advantageous in high performance networks to be able to monitor network performance in real time in order to detect any deterioration of the expected performance. This is especially important in MPLS networks where the minimum performance of a user connection may be specified in a service level agreement between the network operator and the user. Performance parameters of interest include packet loss, end-to-end packet delay, and delay variation.
One method of determining network performance is the collection of statistics by the network nodes. This method can provide summary or detailed packet loss information, but is not appropriate for monitoring delay parameters. This method also requires a great deal of processing of all packets if detailed (per connection) information is to be gathered, and does not lend itself to real time monitoring.
Another method is to send test packets through the network. The disadvantage of this method is that test packets must either have different labels (in an MPLS network) or different IP destination addresses, in order to be distinguishable from the user data. If they have different labels, they require additional network resources (labels are a limited resource) and it would be difficult to guarantee that the test traffic will be subject to exactly the same degradation as the user traffic. If the method is based on different IP destination addresses, additional processing in the forwarding path is required, leading to greater expense or lower throughput.
MPLS provides the general capability of inserting more than one label in each packet (known as a label stack). This capability could be used to provide an additional label to differentiate between the user data stream from the OAM&P packets, but at the expense of the additional label (an increase in packet overhead), and the additional label insertion and decoding step in the edge routers (additional processing in the forwarding path).
Therefore there is a need for the development of the enhanced network and method of transmitting the data through the network, which would provide additional capabilities without using additional resources in the network.